We have previously isolated and partially characterized Alt-1, a major allergen from Alternaria alternata. The present studies involve: 1) additional definition of the physicochemical characteristics of Alt-1; 2) development of immunochemical assays of atmospheric Alt-1 content, to determine whether Alt-1 exists on airborne particulates of such size as to be respirable into the tracheobronchial tree; 3) initiation of an Alt-1 immunotherapy program for Alternaria-sensitive persons, in which the effects of Alt-1 therapy will be compared to those of treatment with either crude Alternaria extracts or placebo preparations; and, 4) development of procedures to measure in-vitro production of IgE antibodies by peripheral lymphocytes isolated from Alternaria-sensitive persons, which will permit investigation of chemically modified derivatives of Alt-1 for their effect on IgE antibody formation.